Concerning others' opinions

I struggle significantly with worrying too much about what others think of me. Often, before posting something online, buying an item, or speaking up in conversation, I question my motives and find that they are seldom genuine but rather stem from a desire to impress strangers or acquaintances. This leads to feelings of insecurity that I try to conceal, even though I am aware of them. My girlfriend frequently asks me why this matters so much to me, but I do not have a clear answer. Despite having a good job and gneerally a decent life, I still feel compelled to care about people's opinions on trivial matters.

I suspect my insecurity stems from unresolved past issues, though I am unsure of their origin. After interactions with others, I frequently second-guess myself, thinking things like "maybe I should have said something different." As a result, I rarely attend social gatherings because the anxiety they cause tends to follow me throughout the night. Sometimes, I take a drink to relax, but the next day I replay every detail of the event, attempting to mentally correct what I perceive as mistakes, even when nothing significant wnet wrong.

I also tell myself that my concern with appearing cool or uncool is exaggerated since others have far more important matters to focus on. Any advice would be appreciated; I am aware this is a long rant but hope it helps explain the situation.